Buggy code:
public class Mutator extends VariableBinder { protected static final int LAST_STATEMENT = Integer . MAX_VALUE ; protected static final int ALLOW_PUBLIC = 1 ; protected static final int ALLOW_PRIVATE = 2 ; protected static final int ALLOW_STATIC = 4 ; protected static final int ALLOW_NON_STATIC = 8 ; protected static final int ALLOW_FINAL = 16 ; protected static final int INHERITED = 32 ; protected static final int ALLOW_VOID = 64 ; protected static final int ALLOW_PARAMS = 128 ; protected static final int VARIABLES = 256 ; private static boolean verbose = false ; protected Map < String , List < String > > prohibitedMethodsPerClass = null ; protected List < String > prohibitedMethods = null ; protected Map < String , List < String > > prohibitedFieldsPerClass = null ; protected List < String > prohibitedFields = null ; public int num = 0 ; public CompilationUnit comp_unit = null ; public FileEnvironment file_env = null ; public Mutator ( Environment env , CompilationUnit comp_unit ) { } public OJClass getType ( Expression p ) throws ParseTreeException { } protected OJClass getSelfType ( ) throws ParseTreeException { } protected OJClass getType ( TypeName typename ) throws ParseTreeException { } protected OJClass computeRefType ( TypeName typename , Expression expr ) throws ParseTreeException { } protected boolean isInnerClassOf ( OJClass a , OJClass b , int options ) { } public String getClassName ( ) { } public String exclude ( String a , String b ) { } public String getMutantID ( ) { } public String getMutantID ( String op_name ) { } public String getSourceName ( String op_name ) { } public String getSourceName ( Mutator clazz ) { } public PrintWriter getPrintWriter ( String f_name ) throws IOException { } public boolean sameReturnType ( OJMethod m1 , OJMethod m2 ) { } public void visit ( MethodDeclaration p ) throws ParseTreeException { } public boolean compatibleMethods ( OJMethod m1 , OJMethod m2 ) { } public static int getMutationsLeft ( ParseTreeObject nl ) { } public static ParseTreeObject getMutationsLimitParent ( ParseTreeObject nl ) { } public Map < OJClass , List < Variable > > getReachableVariables ( ParseTreeObject exp ) throws ParseTreeException { } public Map < OJClass , List < Variable > > getReachableVariables ( Statement exp ) throws ParseTreeException { } private void getReachableVariables ( Statement exp , Map < OJClass , List < Variable > > variables , List < Variable > allVars ) throws ParseTreeException { } private void getMethodDeclarationVariables ( ParseTreeObject exp , Map < OJClass , List < Variable > > variables , List < Variable > allVars ) throws ParseTreeException { } private void addForVariables ( ParseTreeObject exp , Map < OJClass , List < Variable > > variables , List < Variable > allVars ) throws ParseTreeException { } private void addVar ( Map < OJClass , List < Variable > > map , List < Variable > allVars , Variable var ) throws ParseTreeException { } private boolean find ( List < Variable > vars , Variable var ) { } public boolean compatibleAssignType ( OJClass p , OJClass c ) { } public boolean compatibleAssignType ( OJClass p , OJClass c , boolean allowWrappers ) { if ( p == null ) { return false ; } if ( ( c == null ) || ( ( c . toString ( ) . compareTo ( "<type>null" ) ) == 0 ) ) { return p . isPrimitive ( ) ? false : true ; } if ( ( p . toString ( ) . compareTo ( "<type>null" ) ) == 0 ) { <START_BUG> return ( c == null ) || ( ( c . toString ( ) . compareTo ( "<type>null" ) ) == 0 ) ; <END_BUG> } if ( "void" . equalsIgnoreCase ( c . getName ( ) ) ) { return false ; } if ( ( ( p . getName ( ) . compareToIgnoreCase ( "java.lang.object" ) ) == 0 ) && ( ( c . isPrimitive ( ) ) && allowWrappers ) ) { return true ; } if ( ( ( ! ( p . isArray ( ) ) ) && ( ! ( c . isArray ( ) ) ) ) && ( ( ( p . isPrimitive ( ) ) && ( c . isPrimitiveWrapper ( ) ) ) || ( ( p . isPrimitiveWrapper ( ) ) && ( c . isPrimitive ( ) ) ) ) ) { return p . unwrappedPrimitive ( ) . isAssignableFrom ( c . unwrappedPrimitive ( ) ) ; } if ( ( c . isPrimitive ( ) ) && ( ! ( p . isPrimitive ( ) ) ) ) { c = c . primitiveWrapper ( ) ; } return p . isAssignableFrom ( c ) ; } public OJMethod [ ] getInheritedMethods ( OJClass clazz ) { } public OJConstructor [ ] getInheritedConstructors ( OJClass clazz ) { } public OJMethod [ ] getInheritedMethods ( OJClass clazz , int options ) { } public OJConstructor [ ] getInheritedConstructors ( OJClass clazz , int options ) { } private OJMethod [ ] filterPrivate ( OJMethod [ ] methods , boolean filterFinal ) { } private OJConstructor [ ] filterPrivate ( OJConstructor [ ] constructors , boolean filterFinal ) { } public OJField [ ] getInheritedFields ( OJClass clazz ) { } public OJField [ ] getInheritedFields ( OJClass clazz , int options ) { } private OJField [ ] filterPrivate ( OJField [ ] fields , int options ) { } public OJField [ ] getAllFields ( OJClass clazz , int options ) { } public OJField [ ] getAllFields ( OJClass clazz ) { } public OJMethod [ ] getAllMethods ( OJClass clazz , int options ) { } public OJConstructor [ ] getAllConstructors ( TypeName clazz ) { } public OJMethod [ ] getAllMethods ( OJClass clazz ) { }

Fix:
return ( ( c == null ) || ( ( c . toString ( ) . compareTo ( "<type>null" ) ) == 0 ) ) || ( ! ( c . isPrimitive ( ) ) ) ;